Recent years have seen a rapid expansion in the performance of solid state lighting devices such as light emitting devices (LEDs); and with improved performance, there has been an attendant expansion in the variety of applications for such devices. For example, rapid improvements in semiconductors and related manufacturing technologies are driving a trend in the lighting industry toward the use of light emitting diodes (LEDs) or other solid state light sources to produce light for general lighting applications to meet the need for more efficient lighting technologies and to address ever increasing costs of energy along with concerns about global warming due to consumption of fossil fuels to generate energy. LED solutions also are more environmentally friendly than competing technologies, such as compact florescent lamps, for replacements for traditional incandescent lamps.
Adjustment or tuning of color characteristics of light from LED based systems has relied on various LED centric approaches. For example, where a fairly wide range of color selection is desired, the system might use sources that produce light of two or more different colors or wavelengths and one or more optical processing elements to combine or mix the light of the various wavelengths to produce the desired characteristic in the output light. One technique involves mixing or combining individual light from LEDs of three or more different wavelengths (spectral colors such as “primary” colors), for example from Red (R), Green (G) and Blue (B) LEDs. With a LED-centric approach such as LED based RGB, the individual color amounts can be adjusted easily to a wide range of colors, including different color temperatures of white light, in the fixture output. However, using almost monochromatic colors from LEDs as the sources imposes limitations on overall performance. For example, with the approach using LEDs of three different monochromatic colors, the output spectrum tends to have a small number of narrow spikes, which produces a low color rendering index (CRI). It is possible to improve the CRI by providing additional LEDs of different colors, but that approach increases complexity and overall system cost.
Even where some tuning of white light is desired, the adjustment technology has relied on dynamic control of LEDs of different colors. For example, a first type of LED might produce white light of a particular color temperature, either by emission of such light from the device (e.g. by pumping of a phosphor within the LED package) or by pumping a phosphor remotely deployed in the fixture of lamp product. One or more other LEDs of specific wavelength(s), such as red and/or yellow, chosen to shift a combined light output to a more desirable color temperature enable color adjustment. In such an implementation, adjustment of the LED outputs offers control of intensity as well as the overall color output, e.g. color and/or color temperature of white light. However, even this approach may have some narrow spiking in the emission spectrum, e.g. due to the red and/or yellow LED light used to correct the color temperature, and as a result, the color rendering may still be less than desirable.
Solid state lighting technologies have advanced considerably in recent years, and such advances have encompassed any number of actual LED based products, however there is still room for further improvement in the context of lighting products. For example, it is desirable to provide a light output spectrum that generally conforms to that of the lighting fixture or lamp the solid state lighting device may replace. As another example, it may be desirable for the solid state lighting device to provide a tunable color light output of color. It may also be useful for such a device to provide intensity and output distribution that meet or exceed expectations arising from the older replaced technologies. Relatively acceptable/pleasing form factors similar to those of well accepted lighting products may be desirable while maintaining advantages of solid state lighting, such as relatively high dependability, long life and efficient electrical drive of the solid state light emitters.